Automatic iris control



2 Sheefs-Sheet l mmi lsi Owe;

J. J. LAMB AUTOMATIC IRIS CONTROL Filed Sept. 14, 1944 March 18 March 18, 1947. J. J. LAMB 2,417,506

AUTOMATIC IRIS CONTROL Filed Sept. 14, 1944 2 Sheets-Sheet 2 Jags;

3 wue/wtm Jamw JLamb "iii/21111112111111!!! Patented Mar. 18, 1947 AUTOMATIC IRIS CONTROL James J. Lamb, West Hartford, Conn.,'assignorto Remington Randlnc Buffalo,.N. Y., a corporation of Delaware Application'september 14, 1944, Serial No; 554.122

(Cl. 17.8I.7.1)

'2 Claims.

This invention relates to an electronic control means responsive tov variations in light intensity for operating a control'mechanism, and particularly to'means for automatically adjusting the size of'the lens aperture for television apparatus.

The invention compre'hends an electronic control means responsive to variations in light'waves for automatically operating desired apparatus in response to said variations for controlling said light waves or other desired means.

The invention further comprehends the provision of means for automatically setting the iris of an opticalsystem and adjusting its setting during changes'in scene brightness for maintaining a substantially constant illumination level at an image position of said system receiving lightfrom a scene through the iris aperture.

.The invention provides means responsive to variations in amplitude of the viedo signal resulting from variations in scene brightness for automatically adjusting the iris to open and close the opening in the iris for maintaining substantially constant illumination of the photo-sensitive surface or mosaic in the pick-up tube.

The invention further comprehends the provision of means for initially setting the opening in the iris in combination with means responsive to variations in the video signal resulting from variationsin scene brightness for automatically adjusting the setting of the iris for either opening or closing the openingtherein as scene brightness either decreases or increases from the initial brightness to-thereby obtain asubstantially constant level of illumination of the photosensitive surface or mosaic in the pick-up tube.

The invention comprehen'ds the provision of'an automatic-iris adjusting and control mechanism arranged so that the iris may be set initially or at any subsequent time through the operation of manually controlled means for obtaining a desired degree of illumination of the mosaic in the pick-up tube with means responsive to variati onsin amplitude of the video signal for thereafter'adjustingthe iris automatically with variationsin'scene brightness to maintain the desired level of illumination of the photo-sensitive surface or mosaic in the-pick-up tube.

In the drawings:

Fig. '1 is a Wiring diagramillustrating one way of practicing the invention.

Fig. 2 is a fragmentary front elevation of a portion of a television pick-up apparatus or camera illustrating portionsof theinvention.

Fig. v3 is a vertical cross-section taken'on line 3--3 of Fig. '2.

2 Fig. 4 is a'horizontal cross-section taken-on line 4-4 of Fig.3.

Fig. -5 is a detail cross-section taken on :line 5-5 of Fig. 4.

The present invention may be used with any type of television pick-up tube, apparatus, L01 camera. It is customary to provide television cameras with a focusing lens and an iris 'adjust-' able for changing the size of opening for the path of light'focused by the lens on the photosensitive surface or mosaic of a televisiontube." It is usually desirable to adjust the iris ,so'that the opening through the iris will provide for-the passage of the desiredamount of light to obtain an illumination of the photo-sensitive surface or.

mosaic in the tube that will provide the desired contrast in the picture. provides means for setting'and automatically adjusting the iris to produce this result by-usingz the video signal as a means for adjusting the setting of the irisas scene illumination increases" It also provides forusing-a photo-v or decreases. electric cell as a means-for controlling the iris instead -of the video signal so that the invention may be applied to all types of cameras.

The invention'may be applied to any suitable type of television camera or pick-up apparatus which will usually include a casing l as shown in Figs. 2 *to'5 having a front wall 2, bottom wall 3 and side wall 4. The focusing lens ismounted in'an aperture in'the front wall and may'include as a unit an adjustable iris or the iris may be 'a ring member that provides a means for adjusting the size of the iris aperture. For the purpose of the :present invention this ring member is prefera'bly provided with a peripheral groove to re-' 'ceive an endless belt'6 operable for adjusting the iris. Belt 6 is engaged over pulley I mounted on shaft section 8 rotatable in bearing bracket 9' pivotally mounted at I0 on front wall I. A tension'spring ll normally operates bearing'bracket ,9'so as to move it about pivot I 0. and maintain belt Sunder tension for effectively rotating the ring 'of'iris '5in the rotation of pulley"! to adjust the size of the iris opening. Tension spring I 1 has one 'end secured to bearing bracket 9 and the opposite end to the "front wall 2 of casing I.

A suitable shaft coupling l2 connects the free end 'of shaft 8 with one end of shaft section 13 having the other end connected by means of :a'

universal joint M to the end of shaft l5-of limit switch unit l5, shown in Figs. 3 and 4.

The present inwention Limit switch unit l6 has a U-shaped supporting bracket I7. The bottom portion of bracket I1 is secured to side wall 4. Shaft I5 is rotatably mounted in bearing 22 carried by one leg of bracket H in transversely extending relation while the other leg mounts a gear reduction unit l8 having a shaft projecting through the adjacent leg of bracket I! and intercoupled with the free end of shaft 15, as indicated at l9 in Fig, 4. A reversible electric motor 20 is mounted on gear reduction unit l8 while suitable spacin sleeves and screws indicated at 2! are secured to one wall of casing l and gear reduction unit l8 for cooperation with the leg of bracket l! for rigidly supporting the motor and gear reduction motor in the casing.

A pair of snap switches known as microswitches are mounted between the legs on bracket H at one side of shaft I5, as shown in Figs, 8 and 4 and indicated at 23. These snap or microswitches are used in a manner hereinafter described for limiting the rotation of shaft [5 through cntro11ing' the circuit to motor 28 for limiting the adjustment of the iris topredetermined open and closed positions.

The usual form of snap or microswitch constructed in a manner well-known in the art, is used for the limit switches 23. The operating pins of these switches have a resilient strip member 23' engaged over the free end thereof, as shown in Fig. 5. One end of strip member 23' is mounted on the switch body while the free end is engaged over the switch operating pin, one

strip being provided on each microswitch 23.

This provides a means that will efficiently cooperate with the switch operating fingers that will now be described.

A pair of collars 24 and 25 respectively, is secured on shaft in desired positions of adjustment by means of suitable set screws, as shown in Figs. 4 and 5. Collar 24 has a switch-operating finger 26 projecting radially therefrom and arranged to engage resilient strip 23' of one of the microswitches 23, as shown in Fig. 4, for moving the operating pin to disen age the switch and the circuit controlled thereby for opening the circuit to motor 20 at one limit of adjustment of the iris. Collar 25 has a finger 21 formed with an offset end. as shown in Fig. 4, aligned for engagement with the strip 23' of the other microswitch so as to o erate the switch and open the contacts therein for control ing the motor circuit at the opposite lim t of ad ustment of the iris. 'In order to eifect this switch o eration and control of motor 20 it wi l be noted that one of the microswitches is reversed in its position on bracket I! with respect to the other switch. This provides for fingers 26 and 2'! engaging strips 23' in advance of the operating pins in the direction in which t ey r tate in their switch operation so that stri s 23' operate in conjunction with fingers 26 and 21 to cam one of the microswitches into open position.

The television pick-u tube is dia rammatically indicated in the drawin s in all of the views and designated by numeral 3%. The end of the tube provided with the usual photo-sensitive sur face or mosaic. not shown. is directed toward and ali ned with the lens for the camera and in rear of iris 5 in spaced relation as shown in Fig. 4, so that the lens can be adjusted to focus the image of a scene on the photo-sensitive surface or mosaic in a manner well-known in the art. The television pick-up tube 38, shown diagrammatically in the drawings, maybe any suitable type of television pick-up tube now well-known in the art, and will have the various apparatus for operating and controlling the operation of the tube provided in the usual manner. This apparatus will include the usual video amplifier 3! shown diagrammatically in Fig. 1.

The present invention uses the video signal as a means for adjusting the setting of the iris. The amplitude of the video signal is in general proportional to scene brightness, other things being substantially equal. Under these conditions an increase in scene brightness will cause an increase in video signal amplitude and a decrease in scene brightness will cause a decrease in video signal amplitude. It is this variation in video signal amplitude that is used to secure the adjustment of the iris for the purpose of maintaining substantially uniform illumination of the photo-sensitive surface or mosaic in the pick-up tube during substantially wide changes in scene brightness.

The invention provides a circuit arrangement for obtaining the control and adjustment of the iris automatically, and for this purpose, a circuit is made through wire 32 connected to the grid of the last stage of video amplifier 3| through isolating resistance 33 to grid 34 of amplifier tube 35. Grid 34 has a suitable negative bias applied through circuit wire 36 includin isolating resistor 3?.

ing the opposite terminal grounded,

Amplifier tube 35 has a cathode 39 and an anode 4U. Cathode 39 is connected to ground by wire 4|. Anode 45 of amplifier 35 has a wire 42 connecting it to load resistor 43 in turn connected through Wire 44 to the positive terminal of battery 45. The negative terminal of battery 45 is grounded through wire 4'6 comp eting the 52 connected to resistor 53 which is connected in.

turn to an adjustable voltage divider 54. One end of divider 54 is grounded at 55 and the opposite terminal of divider 5 5 is connected to wire 44 to complete the voltage divider circuit and the rectifier c rcuit to cathode 48 through ground 55;

Resistor 53 is the load resistor for the rectifier portion of tube 35. The rectified current through the circuit including cathode 13, anode 5| and resistor 53 develops a varying direct current voltage across the terminals of resistor 53.

The varying direct current voltage in the rectifier portion of tube 35 is filtered in the resistance-capacity filter network indicated at 56..

The operating characteristics of this automatic iris control are governed to a substantial extent by the design of the filter 56 through the selec-' tion of suitable values for the resistances and condensers used in this filter so that the time con stant for desired conditions of operation may be obtained. Filter 56 has an input terminal 51 connected to wire 52 on the anode side of resistor 53. The output terminal 58 of the filter is connected through resistorBS to grid 69 of amplifier tube 6i. Resistor 59 is used to suppress parasitic oscillations. The rectified voltage from the rectifier portion of tube 35 applied to the filter input Wire 36 is connected to a bias battery or other source of voltage supply 33 hav- 5.1. is negative, and therefore appliesanegative voltage to grid 60, negativewithrespectto cathode 62 of tube. 6 I.

Amplifier tube BI is shown in Fig. 1 diagrammatically as a pentode. The difference in voltage between the negative voltage developedby rectified current flowing in resistor 53 and the positive voltage obtained by voltage divider 54 is applied to input 57 of filter 56 and. to grid 65. By varying the adjustment of resistor 54 the positive voltage can be varied tocontrol the amplitude of the direct current voltage'applied to grid fill. This provides a, means of adjusting'the iris to meet desired conditions of operation. The

screen grid 63 is connected to battery 45 for applying a suitable-voltage to establish a desired operating condition of awell-known character used in the operation. of pentodes. The=suppressor, grid 64 is connected to cathode 62 in the usual manner. Cathode 82 is grounded as. illustratedin Fig. 1. v

Anode-65 of amplifier pentode BI is connected by wire 65 through load resistor 61 to wire 44 fornation of the photo-sensitive surface or mosaic in television pick-up tube 39. In addition to setting the position of the iris, this, grid Bil-cathode 52 circuit of tube BI is controlled by variations in amplitude of the video signal through the circuits in the amplifier-rectifier tube 35 through variation of the. amplitudeof the D. C. voltage applied to grid 68 obtained 'by the variation in amplitude in the circuit includingv anode 5! of tube 35. This provides the control for the iris toadjust the setting of the iris to either open or close the opening in the iris inv the adjustment thereof for maintaining substantially uniform. illumination of the photo-sensitive surface or mosaic inv tube 30 during variations in scene brightness fromthat for which the iris is primarily set by the adjustment of resistor 54.

This control for the iris operates through a balanced system for controlling operation of the iris setting means or mechanism.

The means for governing the operation of reversible motor 20 employs a tube 68 which may preferably be in the form of a double triode, that is one having two triode sections. One triode section has cathode 69, grid and. anode II while the other section has. cathode. 12, grid I3 and anode I4.

Awire connected to wire 66, as. shown in Fig. 1, connects anode 65 with grid 10 and wire 16 connected to wire 66 also connects anode 65 to cathode i2, so that all three elements operate at the same direct current potential. A voltagedividing network consisting of resistors T1, 18', i9, 89 and 8i has one end of the network connected to wire for placing it in circuit with the positive terminal of battery 45 and the other end of the network connected to ground at 82 for completing the circuit of the network with the negative terminal of battery 45 through ground connection 45. This voltage dividing network is used to provide the desired potential, positive with respect to ground, for the operation of the circuits connected with the double triode 68. Cathode 69 of tube 58 is connected by wire 83 to the junction of resistors I1, 18' and. 80, so that.

cathode 69- Eat a: higher positive potential than 10;. under resting conditions, that is when there is no change in amplitude of the video signal, the plate current is substantially-zero in each triode section of tube 58.

Anode II of tube 6.3 is connected through wire 85 to solenoidiwinding 85 of relay 87. The other terminal of the winding 85 of: the solenoid is connected through wire 83': to switch blade I28 and contact 89 of switch 90.. Contact" 89 is connected through wireQI to wire. 44 and the positive ter- ;;minal of battery 45. The anode circuit is completed through wires SI, 44-, resistor TI and wire 83 to cathode 69'.

Anode T4 of tube Ill is connected through wire 92 to one end of solenoid winding 83 of relay 94'. H The other terminal of solenoid winding 93 is connected through wire 38 toswitch blade I28 to contact 89 of switch fiiland' then through wire SI to the'positive terminal of battery 45. The anode circuit is completed through Wire 44 and resistor :57 to cathode 1-2.

Relays 8! and IE4 are of the single-pole doublethrow type. The back contact 85 of relay 8'! and backcontact 95 of relay 94 are connected together and to the positive terminal of battery 91 through 5-wire98'. The other terminal of battery 91 is connected to ground as indicated at 99. When solenoid windings 86 and 53* are not energized, armature Hit of relay 54 connects contact 96 through wire I82 to switch blade I93 of switch Si! and armatureiiil of relay 81 connects contact 95 through wire I02 to switch blade IE3 of switch 90.

Contact Ifl l of relay 94 is connected to switch Hi5, a normally closed switch of the spring action when armature IIJII makes contact with contact Mi t-of relay 94;

Switch I I3 in Fig. 1 isthe other limit switch 23 shown in'Figs. 3 and 4- and is connected in series with contact I I2 of relay 531, inductor I I4 and field coil i I5 of motor to; The'other terminal of field coil H5 is connected tomotor-armature its at I59; When relay arr-nature Iii! makes contact with contact H2, motor field H5 and armature I fie-are energized by battery 97. Field coils lo! and I 95' of'motorZIl are oppositely wound so that the direction of rotation" or'armature its is dependent upon the selection of the desired field coil. Condenser lid is connected between the grounded terminal of armature 558 of motor iii and the junction of field coil IIli and inductor I lit; Condenser iIBis connected between the grounded terminal of armature I58 and the junction of field coil H5 and inductor IM. Condensersl I5 and I It in conjunction with inductors IIlIii and H4 suppress electrical disturbances aristype generally lmown-in the art as a microswitch.

ing from sparking at the commutator brushes of armature I08 in a manner well-known in the art. Condenser I I9 connected between connection I99 and a ground at I20, and resistorIZI connected between connection I69 and ground I22 provide additional suppression of disturbances arising from sparking at the commutator brushes. Limit switches I85 and H3 are operated by fingers 25 and ill on shaft I5 during adjustment of the iris in such a way that when the lens iris has been closed to a selected limiting value by motor 29 switch I I3 is opened by the fingerZE for example, thus disconnecting motor 2%! from battery 9'1. When the lens iris has been opened by operation of motor 25 to a selected limiting value, switch 105 is opened for example, by finger 21, disconnecting motor 20 from battery 91.

Resistor i23 is connected to armature I of relay 94 through wire Hi2. Resistor I24 is connected to armature Iill of relay 8! through wire I82. The opposite terminal of resistor I23 is connected through wire I25 to contact IM while the other terminal of resistor I 24 is connected through wire I26 to contact H2. Resistors I23 and I24 are connected across the relay contacts of relays 81 and 94 to suppress sparking at the relay contacts on making and breaking the circuit. A condenser I2! is connected to contacts 95 and 95 through wire 9% and the op osite terminal of the condenser is grounded at I29. Condenser 42! cooperates in the suppression of the sparking or arcing at the relay contacts.

Switch Bil provides a means for changing from manual to automatic control of the adju tment for the lens iris. Switch 90 is of the double-pole double-throw type, with blades Ill3 and I23 acting together. With switch 90 in a position where blade 128 makes contact with contact 38, relays 61 and 94 and anodes II and 84 of tube 53 are connected to batterv 45 so that tubes 68 receive power so that the circuit through anodes II and M are energized. Blade I83 of switch 8%! makes contact with switch terminal Is!) having no circuit connection.

When switch so is in such a position that blade I83 makes contact with contact I3I, wire I02 is connected to switch blade I32 of the switch indicated at 33. Simultaneou ly switch blade I28 of switch 9a is in contact with contact I34 disconnecting the circuit through wires 88 and 9! and battery d5. relays 81 and 94 together with anodes 7i and M of tube 68 so that tube 83 and the circuits associated therewith for controlling mo or 26 will be deenergized.

With contact I 3! and armature I03 of switch 9!) in contact, power from battery 91 may be appl ed to motor 20 through wire I35 to field coil I I by setting switch I33 so that switch blade I32 makes contact with contact I31. The po er may be a plied to operate motor 20 through field coil ill! by moving switch blade I32 of switch I to engage contact I35 to complete the circuit throu h wire #25 to contact KM. Manual operation of switch I 33 may therefore be used when switch 90 is operated to the manual control position for securing adjustment of the iris to or toward either open or closed positions. This manual adiustment of the iris is obtained independently of the automatic setting and control thereof.

In operation. the iris first is set to the desired positionthrough adjustment of variab e resistor 56. Then in the subsequent operation of the television pick-up apparatus, the amplitude of the video signal which is in general proportional to scenebrightness, other things being equal, will serve'to control and produce automatic adjustments of the iris with changes in amplitude of the video signalcaused by changes'in scene I brightness. As above pointed out, an increase in tive direct current voltage at grid 60 of tube El to increase. This in turn causes the anode current of tube 6| to decrease, with the result that the voltage drop across resistor 61 also decreases since this resistor is part of the anode circuit of tube SI. Since the direct current voltage between grid !0 and cathode 69 of tube 68 is equal to the difference between the positive (with respect to cathode 69) voltage "drop across resister 1? and the negative voltage drop across resistor 51, a decrease in voltage drop across resistor BI will cause the voltage at grid III to become more positive with respect to cathode 69. Consequently the current in the circuit including anode l! and cathode 59 will increase. When the increment in current to anode II becomes sufliciently large, relay 8! will operate by solenoid winding 55 being energized to move armature I 9! into engagement with contact II2 for closing the circuit through field coil H5. This energizes electric motor 20 to operate in one direction to adjust the iris toward closed position through the rotation of pulley I by the shaft connection thereof with the motor and the adjustment of the iris through movement of belt 6. As the lens iris closes, the intensity of illumination on the photo-sensitive mosaic of the television pick-up tube 30 decreases, thereby decreasing the amplitude of the video signal. Thus the negative direct current voltage at grid 68 of tube 5! decreases; the anode current in the circuit including anode 65 of tube 6! increases, the voltage drop'across resistor 61 increases, grid ID of tube 58 becomes less positive with respect to cathode 69, and the current in the circuit including anode 'lI, cathode 69 and solenoid winding 83 decreases. This process continues until the current decreases to a value which deenergizes relay 83' to open the circuit at armature IUI and contact IIZ thus disconnecting motor 20 from the source of electrical energy Bl. When this occurs motor 26 ceases rotation and the lens iris remains in adjusted position. ,Since the initial balance of the system was based on a video signal of selected value, as determined by the setting of variable resistor 54, the new setting of the iris will be one in which the illumination of the mosaic in the pick-up tube will have a value that will result in a video signal of the initial value. The control therefore automatically maintains constant video signal output under increasing scene brightness within the limits of adjustment of the iris for changing the size of the aperture therein by reducing it to a minimum size.

When scene illumination decreases the resulting decreased video signal will cause the negative direct current voltage at grid Gd of tube El to decrease, thereby increasing the current in the circuit including anode E5 of tube 6|. Thus the voltage drop across resistor 51 increases. The direct current voltage between grid I3 and cathode 52 of tube 68 is equal to the algebraic sum .of.- the voltage dropacross resistor I8 (negative .with respect to cathode 12), resistor 11 (negative with respect to cathode 12), and resistor 67 (positive with respect to cathode 12). Therefore when the voltage drop across resistor 61 increases, grid "F3 becomes more positive with respect to cathode J2, causing an increase in the current flowing in the circuit including anode 14,

cathode l2, and solenoid winding 93 of relay 94. When the increment of current in this circuit becomes sufficiently large, relay 9% will operate, operating armature loll to engage contact Hi l thereby closing the circuit through field coil I831 of motor as for securing operation of the motor. The motor will operate to open the iris by means of the rotation of shaft 8, pulley i and operation of belt 6. As the iris opens the illumination on the pick-up tube mosaic increases, causing an increase in the video signal. As a result, the negative direct current voltage at grid til of tube 6! increases, the anode current of tube 6| through anode 65 decreases, the voltage drop across resistor ii'l' decreases, the direct current voltage at grid 13 becomes more negative and the current in the circuit including anode M, cathode and relay solenoid winding '53 decreases. As the motor continues to open the iris this process continues until the current through relay solenoid winding decreases to a value that causes the relay to open, breaking the motor circuit between armature [do and contact 5&4 when motor rotation will cease and the iris will remain in adjusted position. At this point the video signal amplitude is that determined by the initial setting of variable resistor 55 thereby obtaining automatic control of the iris for maintaining constant video signal output under conditions of decreasing scene brightness within the limit or" the maximum degree of opening of the iris.

It will therefore be understood that the opening in the iris may be initially set by adjustment of variable resistor 5 for a desired intensity of illumination of the mosaic in tube 33 for a given scene brightness and that when scene brightness varies thereafter in the operation of the television pick-up apparatus, the variation in scene brightness causing a change in amplitude of the video signal will secure operation of the motor 26 to automatically adjust the iris toward either open or closed positions to maintain substantially uniform illumination of the mosaic in the pick-up tube.

The circuit connected with tube. 68 provides a pair of independent but intercoupled operating circuits or operating means for securing operation of motor 2i) through the cooperation of relays 8i and 9d. The anode circuit of anode 6-5 of tube 6| being intercoupled with both triode sections of tube t8 is arranged to control the balance between the tWo operating circuits for the relays 81 and 94 for securing and maintaining the initial adjustment of the iris in accordance with the setting of variable resistor 5d and in addition provides a control means for securing operation to adjust the iris through the variations in amplitude of the video signal being transmitted and impressed upon the circuit including anode 65 hereinabove described to secure operation of motor 2i! for adjusting the iris to both increase and decrease the size of the lens aperture. Tube 35 with its amplifier and rectifier portions operates through the rectifier portion including the circuit with anode 5! to provide a control means for controlling iris adjustment for obtaining the desired lighting of the mosaic in the pick-up tube 30, and maintaining this illumination in a sub- 'stantially constant manner through variations in scene brightness by using changes in amplitude of. the videosignal impressed upon the circuit including anode 5! for securing energization of .iens aperture by connecting the output of such a cell ,to grid 35% or grid 60 and using the remainder of the Wiring connections and apparatus as shown in Fig. 1 and described above.

The word iris as used in the foregoing description and in the claims shall be interpreted to (define a device for controllingthesize of aperture for light passage through a lens of an optical system that may be operatedto vary the size of said aperture in any suitable manner for controlling the character of illumination of an image so that a uniform image illumination may be obtained with variations in scene brightness. The word iris shall be further interpreted to define any spatial electromagnetic wave attenuating device such as a light filter or plurality of light filters interposed in the transmission path of such wave.

The word light as used in the foregoing description and in the claims shall be interpreted to define electromagnetic waves in both the visible and invisible portions of the electromagnetic wave spectrum, including ultra-violet and infrared waves.

It is to be further understood that the motor hereinabove described may drive any type of control device such as a rheostatconnected in circuit with the light source to control the light source for obtaining uniform illumination rather than to control the light reaching the brightness variation sensitive element. Or the control voltage may be applied to the input circuit of one or more electron tubes, known as Thyratron tubes, to control the power applied to electric lamps connected to the output circuit of said electron tubes. In fact, the operating means herein described may be used to operate many different types of variable controlling apparatus where it is desired to introduce an automatic control of apparatus that varies in operation so as to maintain a substantially uniform condition of operation of such apparatus. The invention uses a potential'variable with the variation in operation of the means to be controlled and with the initial control setting means obtains an automatic control of the operation to obtain a substantially uniform and desired condition of operation.

The invention claimed is:

1. Ina television pick-up apparatus having a pick-up tube, a video amplifier and an adjustable iris for controlling the light intensity focused on the mosaic of said pick-up tube, the combination of a reversible electric motor connected to adjust said iris to enlarge and reduce the size of the opening therein in rotation thereof in opposite directions, a pair of electro-magnetic operated means each controlling operation of said motor in one direction, a double triode having a pair of normally balanced circuits coupled therewith each controlling one of said electro-magnetic operated means, and circuit means responsive to variations in amplitude of the video signal coupled with said double triode for unbalancing one of said pair of circuits to secure motor operation for adjusting said iris to maintain a substantially uniform video signal amplitude during variations in scene brightness.

2. In a television pick-up apparatus having a pick-up tube, a video amplifier and an adjustable iris for controlling the light intensity focused on the mosaic of said pick-up tube, the combination of electrically actuated iris setting means, an electrcnic control system having a pair of input and output circuits, each output circuit coupled to electrically operate said setting means in one direction for operating said iris to either open or close the lens aperture, said input circuits being coupled to control both output circuits, one input circuit having means coupled therein to secure operation at a constant potential, an amplifier having an output circuit coupled with the other of said input circuits for varying the potential thereof relative to the potential of said firstmentioned of said input circuits, said amplifier having an input circuit including means adjustable for setting the voltage amplitude therein and setting the iris for a desired illumination of the mosaic, and an electronic operated means responsive to variations in video amplitude for impressing said variations on said amplifier input circuit for varying the voltage amplitude therein whereby said iris will be adjusted in response to variations in amplitude in the video signal for maintaining a substantially uniform video signal during variations in scene brightness.

JAMES J. LAMB.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,133,882 Zworykin Oct. 18, 1938 Re. 22,508 Krutzler et a1 June 2'7, 1944 1,942,587 Whitman Jan. 9, 1934 FOREIGN "PATENTS Number Country Date 444,074 British Mar. 12, 1936 

